[14a-2Q-1~13] 9.2 Nanowires and Nanoparticles

▲ [14a-2Q-11] Size dependence in the electronic structures of fcc- and hcp-type Ru nanoparticles

〇(P)Rosantha Kumara¹, Osami Sakata¹, Anli Yang¹, Kohei Kusada², Hirokazu Kobayashi², Hiroshi Kitagawa² (1.NIMS/SPring-8, 2.Kyoto Univ.)

Keywords:nanoparticles,electronic structures,catalysts

Recently, research interest has shifted to transition metal nanosized catalyst since they show an improved activity due to the greatly increased surface to volume ratio compare to their bulk-counterparts, which is beneficial for catalytic applications. Ru is a 4d transition metal that in the bulk adopts an hcp structure at all temperature ranges, and novel fcc-type Ru nanoparticles (NPs) have been observed to be more efficient than conventional hcp-type Ru NPs larger than 3 nm. It has recently attracted much attention as a potential application in removal of car exhausts due to high catalytic activity for CO oxidation and preventing CO poisoning in fuel-cell system. Size dependent changes in the optical, structural, and electrical properties are related to the basic changes in the electronic structure of nanosized materials. Hard X-ray photoelectron spectroscopy (HAXPES) can provide important information on the influence of nanoparticle size on electronic properties. The HAXPES measurements were performed at the BL15XU of SPring-8. The incident X-ray energy used was at 5.95 keV, while the total energy resolution was set to 240 meV. The corresponding inelastic mean-free-path (IMFP: λ) is about 5.8 nm for Ru according to the TPP-2M formula. HAXPES Ru 3p core-level spectra of fcc- and hcp-type Ru NPs and bulk Ru show that two Ru 3p_3/2 and 3p_1/2 peaks at 461.8 and 483.8 eV, respectively. The peak at around 461 eV has been attributed to Ru (0) from metal atoms. There was no any significant different of binding energies of Ru 3p core-level of NPs with size and structure. In particular, there is notable increase of peak width compare to the Ru bulk materials. In this study, the observed trend of increasing catalytic activity of fcc-type Ru NPs was discussed using their core-levels and valence band spectra, to gain further knowledge about CO oxidation catalysts behavior.